I. Field of the Invention
The present invention relates to a system for controlling the shape of strips or sheets.
The invention is readily applicable for use at mills for cold or hot rolling of strips or sheets where automatic control or regulation of their shape is effected.
The strip or sheet being rolled tends to have irregularities in its shape, such as edge buckles or crowns, caused by the ever-changing rolling conditions (a roll force, overdue tensioning, rate of rolling, displacement of the housing screw, alterations in thickness or cross section of the strip or sheet being fed, a distribution of temperature lengthwise of the roll body). In order to avoid the irregularities in the shape of the rolled strip or sheet, it has been employed in the art automatic control systems the application of which presents some difficulty in carrying out effective control of the shape of the strip or sheet being rolled.
For example. U.K. Pat. No. 1,290,096 describes a device for controlling the shape of a strip or sheet being rolled, which comprises reference means or a light source spaced from the strip or sheet which is being rolled and disposed at a right angle relative to the longitudinal direction thereof, a TV camera for viewing or quantitatively detecting a virtual image of said reference means formed by the reflection upon the reflecting surface of the said strip or sheet, detecting means for detecting the deviation of the virtual image representative of the middle and end portions of the strip or sheet being rolled from a predetermined reference, and hydraulic pressure means for correcting the roll camber of a pair of working rolls in response to the output from said detecting means.
To enable effective operation of the above-described device, it is necessary to remove water (emulsion) and oil from the surface of the rolled strip or sheet, which, if unremoved, cause the light beams falling on the strip or sheet to refract, thus permitting error or distortions to occur in the measurement of the strip or sheet shape. In addition, aggressive ambient atmosphere of rolling mills impairs operating efficiency of the optical and TV instruments employed in the device.
There is also known a device for controlling the shape of a strip or sheet being rolled (see "Shape Measurement and Control", by W. K. Y. Pearson, B.Sc. Journal of the Institute of Metals, 1964-65, vol. 93, p. 169-178), comprising rollers positioned transversely on both sides of the strip or sheet and brought in contact therewith at the exit from a roll mill stand, with the shape of the rolled strip or sheet being controlled in accordance with alterations in the rotational speed of said rollers. Operatively connected with the rollers are selsyns which form the output signal in response to the disagreement in the rotational speed of the rollers. There are also provided means for detecting the travelling speed of the strip or sheet, a means for correcting the shape of the strip or sheet being rolled, a means for detecting irregularities in the shape of the strip or sheet being rolled, a computer having its inputs connected to the selsyns and to the means for detecting the travelling speed of the rolled strip or sheet and its output connected to the means for correcting the shape of the rolled strip or sheet and to the strip or sheet shape indicator.
However, the device described above is disadvantageous in that the strip shape output signal is formed with a substantial time lag (up to 1 sec), since the time of operation of the strip-shape controller and the strip travelling-speed sensor, built around selsyns, servomotors and tachogenerators, is not rapid enough to embrace the entire operating range of deviations in the shape of a strip or sheet being rolled.